For Quackers or Mormons, nothing short of ASB would do, unless, the population of China is literally reduced to a fraction. Alternatively, couple this with the kind of US regime that would actively persecute a religion very popular in the US... adherents of said religion run, of all places, to China, where they are extremely successful, especially if they get there at the time when the Chinese leadership has not fully asserted control of the country. By the time the leadership decides to do something about it, there are simply too many converts, and the country's leadership decides that conversion is the lesser of two evils, as long as their own doctrines are not being contradicted.
Or, make someone like William Penn take his followers to China, and try to make mass conversions there. Who knows, they might even succeed, and the timeframe would allow for Quacker faith to spread enough to be a major factor in China, religiously speaking.
Of course, there is always the faith in the HOLY
SHEEP!!!
Now that should be a challenge to make that the official religion of China... or any country for that matter